282 BOTANICAL GAZETTE [ocToBER 
The general distribution and topography of the mechanical tissues 
of the sporangium may be learned from the somewhat diagram- 
matic illustration appearing as fig. 17. This figure will be dis- 
cussed more fully at a later stage. The anatomical details of 
organization of the microsporangium of Ginkgo, as illustrated by 
photomicrographs, may iently be taken up here. Fig. 1 
shows a vertical section through one of the microsporangia. At 
the lower side are spores lying within the sporangial cavity. Trans- 
versely in the upper region of the figure runs the termination of 
one of the fibrovascular bundles of the sporophyll. The bundle 
is accompanied on its upper side by short transfusion cells, such 
as are characteristic of the gymnosperms. These appear as reticu- 
lated elements. To the right and separated from the transfusion 
tissue by two elongated unsculptured cells is the bundle proper, 
with its protoxylem elements uppermost and the larger elements 
of the metaxylem beneath. Toward the left the bundle as a whole 
ends in transfusion elements, a situation often present in the 
gymnosperms. The transfusion cells commonly become imper- 
ceptibly merged into the fibrously thickened cells which constitute 
the mechanical tissues of the sporangium wall. Fig. 2 presents 
another and less favorable view of the same features. 
Fig. 3 reproduces a horizontal section through the petiole of 
the sporophyll and the two sporangia. Right and left lie groups of 
spores indicating the position of the spore sacs, while in the center 
is a fan-shaped mass of tracheids marking the termination of the 
fibrovascular strands of the sporophyll in a complex of transfusion 
tracheids. To the right and left of the fan lie cells with elongated 
nuclei, which mark the position of the two strands of phloem 
ending in the bases of the sporangial cavities. Fig. 4 reproduces a 
portion of the right of fig. 3, more highly magnified. The gradual 
passage of the transfusion elements into the cells which constitute 
the mechanical system of the sporangium wall can now easily be 
distinguished. To the extreme right are spores in the cavity of 
the sporangium, and below these, to the right of the transfusion 
cells, are to be seen two elongated nuclei belonging to the phloem. 
Returning now to the radial longitudinal view of the vascular sup- 
ply of the sporangium, in fig. 5 we see under a somewhat high degree 
